The economic disposal of waste solids and recovery of clean water from aqueous solutions and dispersions thereof is a recognized problem. Also, the need to recover clean water and valuable solid materials from aqueous solutions and dispersions thereof is a common occurrence. Ideally, apparatuses and processes for the recovery of water from aqueous solids should provide ease of disposition of all constituents, avoidance of pollution, economic operation and hygienic handling, and should, in addition, yield clean water. Furthermore, in the course of recovering clean water it is desirable to obtain by-products, both solid and liquid, which are valuable in themselves or can be utilized to further the economics of the process. For purposes of this invention it is to be understood that the term "aqueous solids" is employed generically to include suspensions, dispersions, solutions, mixtures and other forms of fluid association of solids in water.
In our U.S. Pat. No. 4,270,974 titled "Process and Apparatus for Recovering Clean Water and Solids from Aqueous Solids" are described process and apparatus whereby aqueous solids are mixed with a low viscosity, relatively volatile, water-immiscible light fluidizing oil to form a mixture which is dehydrated by heat evaporation. The dehydration step is accomplished in a plurality of sequential heat evaporation steps wherein each of the successive heat evaporation steps is at a successively higher temperature and the resulting solids streams are of successively higher concentration because of increasing dehydration, the evolved vapors of each evaporating step supplying a substantial portion of the heat requirement of the preceding heat evaporation step. Despite the use of a relatively efficient multiple stage heat evaporator, the energy requirements are substantial. For example, the energy usage of a four-stage heat evaporating system dehydrating a 15-20% solids input is typically around 400 BTU's per pound of water evaporated.